Gary Turner <kk5st@swbell.net> writes:
> The Gimp works at 72 or 96 ppi(pixels per inch).
No, it doesn't. This is one of the most commonly held misconceptions
about digital resolutions.
First, about image resolution. There's a tag within most image
formats which contains the number of pixels per inch each way. When
scanning, the scanning software usually puts a value in here which
lets you figure out how big the original was.
The ppi[1] value only makes sense if you're trying display something
to a certain physical size. So it matters when you want a certain
size print, or when you want a certain physical size print on your
monitor (ie, you want to match the size of a print).
In the Gimp, you can set or change the ppi value in the Scale Image
dialog. If you just change the stuff in the "Print Size & Display
Unit section, you aren't changing anything about the image, just those
tags I mentioned earlier.
What does the gimp work at? The Gimp has two modes: first it can work
in "dot-for-dot" mode, where 1 dot on screen corresponds to one dot in
your image. The zooms will then work on dots. Reduce it to half
size, and it'll show half dots.
Turn off dot-for-dot mode, and the Gimp will display images on your
monitor the same size they should be on paper, according to the ppi
tags. If you have a 100ppi monitor, and you're viewing a 300ppi
image, at 1:1 mode the Gimp will scale the 300ppi image down to 100ppi
for view, so it's the same size it would be elsewhere.
Gimp knows the real image resolution of your monitor from the
File->Preferences->Monitor. It's probably not 72ppi or 96ppi. Mine,
for instance, is 116ppi. The Gimp has a way to calibrate your so you
can get a ruler and figure out the size.
Back to the original poster's question, if it was scanned from film,
either it was scanned at a really high resolution and gimp doesn't
think it's reasonable, or Walmart didn't put real information in those
tags. Who knows... it's a benign error anyway, since you probably
don't care about displaying an image on screen the same size as a 35mm
film frame. (For a similar reason, the ppi info coming from digital
cameras is similarly useless.)
--
Alan Shutko <ats@acm.org> - In a variety of flavors!
5.25" floppy is not better than 3.5" hard.
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